1. Field of the Invention
The present invention relates to hydraulic systems that control operation of a hydraulic cylinder, and more particularly to a valve arrangement and method incorporating a regeneration function for controlling operation of such a hydraulic cylinder.
2. Description of the Related Art
In excavating machinery and other heavy equipment and equipment hydraulically controlled generally, controllability and efficiency are several metrics that can be used to quantify the profitability and operator “feel” of the machine.
As a normal machine metric, operators can test for cavitation of functions. Cavitation is an unwanted condition that can occur when a function has an overrunning load. In an excavator, for example, the hydraulic cylinder used to control the excavator arm is susceptible to cavitation due to the arm having a large amount of potential energy when it is fully out, and the cylinder has a rather large cylinder area to fill with hydraulic fluid as the arm comes in towards the excavator.
One method to keep the arm from cavitating is to use regeneration of the arm cylinder where some of the rod exhaust fluid is pushed back into the head of the cylinder to help makeup (regenerate) fluid as the head chamber is expanding. This requires a connection from the rod side of the cylinder to the head side of the cylinder and normally a smaller connection from the rod side of the cylinder to the tank.
However, when the excavator is digging, the head side of the cylinder can have a higher pressure then the rod side of the cylinder, which does not allow for regeneration. Therefore, all of the rod fluid must go to tank through the smaller rod side to tank connection. This causes a large differential pressure across the control valve, which results in a high rod side pressure. This rod side pressure works against the head side pressure when digging, which reduces the force and efficiency of the machine.
Hydraulic circuits have attempted to better control the regeneration function by sensing pressure at the fluid source to determine if regeneration should occur. Based on the sensed pressure at the fluid source, the circuit can open a secondary passage to reduce the differential pressure across the control valve. Yet, these circuits still fail to provide better control for regenerating as the sensed pressure at the fluid source does not always provide the appropriate pressure value for determining when regeneration should occur.
Therefore, there is a desire to provide an improved valve arrangement incorporating a regeneration function for controlling operation of such a hydraulic cylinder.